Silicon carbide (SiC) has become the material of choice for next generation high power electronic devices [1]. There are ongoing efforts to optimize the PVT growth process to obtain 150mm wafers with lower dislocation densities. The latter include threading screw mixed dislocations (TSDs/TMDs), as well as basal plane dislocations (BPDs). Prismatic slip systems were observed in SiC wafers. They were formed when threading edge dislocations (TEDs) lying in prismatic planes glide under the influence of radial thermal gradient stresses. Screw dislocation segments were left in their wake that can then cross-slip onto the basal plane. Previously, we reported on a radial thermal model of the PVT growth process developed to predict the distribution of prismatic slip [2]. This model, based on a cylindrical boule, predicted the occurrence of slip in different prismatic planes as function of radial position in the boule. The predicted distributions showed good correlation with observed distribution on X-ray topographic clearly demonstrating the role of radial thermal gradients in activating prismatic slip during PVT growth. Current studies, however, indicate surface-related prismatic slip nucleation at work, and an update from the cylindrical model to include the growth interface curvature complexity was needed to help further describe the behavior. Recent X-ray topography studies of 4H-SiC wafers reveal that during early stages of boule growth when the growth interface is relatively flat, prismatic slip dislocation distributions correlate well with the predictions of the previous thermal model [2] with high dislocation densities near the peripheral regions dropping to zero near the center (see Fig. 1(c) for wafer sliced from early stages). However, during the later stages of growth the dense distribution predicted by this model overlays a less dense distribution of prismatic slip dislocations that extends all the way to the center. This is observed in the wafer shown in Fig. 1(b) taken from later growth stages when the growth interface was more convex. The curved boule interface is composed of steps and terraces that will tend to form macrosteps. As the curvature increases, the resulting thermal profile at the growth interface was observed to result in sufficient thermal stresses to nucleate and propagate dislocations half loops from the surface steps (Fig. 2). In particular, kinks on the vertical step risers of the macrosteps may act as sites for nucleation of half loops on prismatic planes while the junctions between step risers and terraces can introduce BPD half loops. Additionally, the asymmetrical step configuration produced by off-axis growth can result in an asymmetrical distribution of prismatic slip due to the interface-shape mechanism. Manipulating the interface shape can make it vary from concave to convex with other complex shapes in between, having an effect on suppressing the prevalence of curvature-related prismatic slip generation when the surface curvature is lessened. Said another way, a higher radius of curvature reduces the contribution of surface prismatic slip generation. Based on these observations, a modified 3D axisymmetric thermal model using finite element methods that incorporates the shape of the interface is deployed and predictions of this model at different stages of growth will be presented and correlated to observations in wafers sliced from corresponding parts of the boule. Such studies can help optimize the growth to minimize occurrence of prismatic slip as boule diameters are increased to 200mm and beyond.